Composite material panels are used in many different applications, including automobiles, airplanes, housing and building construction. The properties sought in such panels are strength, rigidity, sound absorption, and heat and moisture resistance. One application of such panels which has been especially challenging is automobile headliners and other automotive interior panels. Many different types of laminates and laminated composites have been tested and produced for use in automobiles. Some headliners have a core of fiberglass fibers and a polyester resin. Others have been manufactured from a core of open cell polyurethane foam impregnated with a thermosetting resin, and with a reinforcing layer of fiberglass. This type of construction is inefficient in mass production, and has low acoustical attenuation which is particularly undesirable for automobile headliners.
Other approaches have been to form a laminate of fiber reinforcing mat, such as a glass fiber mat on a fibrous core, and a second reinforcing mat on the opposite side. The exposed surfaces of the reinforcing mat are then coated with a resin and an outer cover stock applied. This laminate is then formed to a desired shape under heat and pressure, i.e., compression molding. Although this type of structure has somewhat improved acoustical characteristics, additional sound dampening is desired, particularly for luxury automobiles.
In the prior art, the fibrous layers of the laminates consist of fibers of relatively large and uniform denier or size. This parameter is critical to sound attenuation properties, and fibers of finer or smaller denier are required to achieve greater sound absorption. However, fine denier fibers in the range of 1.2 or less lack the resiliency required for retention of thermoformed shapes. Although resiliency can be achieved by impregnating the fibers with a resin, it is very difficult to impart an even distribution of resin into a fibrous batt containing fine denier fibers. In the prior art, extensive impregnation of the fibrous layers was not required due to the presence of the stiff reinforcing layers. Hence, given these trade-offs, a truly superior acoustical dampening headliner of sufficient strength could not be produced.
Although layers containing fiberglass have the desirable characteristics of strength and some sound attenuation, they have the undesirable traits of reflecting sound when made very hard or dense. Fiberglass, particularly in woven mat form, is also difficult to handle and is a known skin irritant. Because the production of headliners and similar panels using fiberglass is most commonly done manually, this is a significant problem which has not been addressed. Alternative fibers, natural and synthetic, have not been developed to be both cost effective and have strength comparable to glass.